1. Field of the Invention
The present invention relates to a spin valve magnetoresistive film comprising a free ferromagnetic layer, a non-magnetic spacer layer contacting the free ferromagnetic layer over a first interface, and a pinned ferromagnetic layer contacting the non-magnetic spacer layer over a second interface. In particular, the invention relates to a so-called current perpendicular-to-the-plane (CPP) structure spin valve magnetoresistive head allowing a sensing current to flow through the spin valve magnetoresistive film in a direction perpendicular to the first and second interfaces.
2. Description of the Prior Art
As well known, the larger the number of giant magnetoresistive (GMR) films gets within a current perpendicular-to-the-plane (CPP) structure magnetoresistive head, the larger variation in the electric resistance can be detected in the overall CPP structure magnetoresistive head. A larger variation in the resistance of the CPP structure magnetoresistive head is allowed to greatly contribute to reduction in the magnitude or level of a sensing current. Specifically, the CPP structure magnetoresistive head is allowed to accurately detect the magnetic bit data with a smaller or lower sensing current. In particular, a larger variation in the resistance can be obtained in the CPP structure magnetoresistive head irrespective of reduction in the core width. A smaller core width leads to a higher density of recording tracks. The CPP structure magnetoresistive head of this type is supposed to greatly contribute to realization of a still higher recording density in the field of a magnetic recordation.
However, the increased number of GMR films in the aforementioned manner inevitably suffers from a deteriorated or lower linear recording density along the recording tracks. An expected improvement in the recording density cannot be achieved. Moreover, the CPP structure magnetoresistive head of the aforementioned type also suffers from difficulty in controlling the magnetic domain of the free ferromagnetic layer.
It is accordingly an object of the present invention to provide a CPP structure spin valve magnetoresistive transducer capable of achieving a larger variation in the electric resistance with fewer layers.
According to a first aspect of the present invention, there is provided a current perpendicular-to-the-plane (CPP) structure spin valve magnetoresistive (MR) transducer comprising: a free ferromagnetic layer; a non-magnetic spacer layer contacting the free ferromagnetic layer over a first interface; a pinned ferromagnetic layer contacting the non-magnetic spacer layer over a second interface; and an insulating layer spaced by the pinned ferromagnetic layer from the non-magnetic spacer layer.
In addition, according to a second aspect of the present invention, there is provided a current perpendicular-to-the-plane (CPP) structure spin valve magnetoresistive (MR) transducer comprising: a free ferromagnetic layer; a non-magnetic spacer layer contacting the free ferromagnetic layer over a first interface; a pinned ferromagnetic layer contacting the non-magnetic spacer layer over a second interface; and an insulating layer spaced by the free ferromagnetic layer from the non-magnetic spacer layer.
Any of the CPP structure spin valve MR transducers as described above enables the rotation of the magnetization in the free ferromagnetic layer in response to the reversal of the magnetic polarity applied from the outside. The rotation of the magnetization in the free ferromagnetic layer in this manner induces a larger variation in the electric resistance of the spin valve MR transducer. When a sensing current is allowed to flow in the vertical direction perpendicular to the first and/or second interfaces, a variation in voltage or the like appears in the sensing current, depending upon the variation in the electric resistance.
In this case, the sensing current is allowed to penetrate through the insulating layer in the CPP structure spin valve MR transducer. Fine pin-holes generally formed in the insulating layer are supposed to enable migration of electrons through the insulating layer. The sensing current thus concentrates at the individual pin-holes. Accordingly, similar to the situation in which the sensing current is allowed to flow through a reduced sectional area, a larger variation can be obtained in response to the inversion of the magnetization in the free ferromagnetic layer in the spin valve MR transducers of the above-described types. The CPP structure spin valve MR transducers are thus expected to greatly contribute to realization of a still higher recording density as well as a reduced consumption of the electricity. Moreover, the spin valve MR transducers of the above-described types are expected to exhibit an electric resistance approximately equal to a tenth part of that of a well-known tunnel junction magnetoresistive (TMR) element. Accordingly, a thermal noise can significantly be suppressed in the spin valve MR transducers as compared with the TMR element. It should be noted that the sensing current is only required to have at least a component flowing in the direction perpendicular to the first and/or second interfaces.
The insulating layer is only allowed to include a compound consisting of at least elements of two kinds. The compound may include an oxide, a nitride, a carbide, a boride, and the like. The insulating layer may be interposed between a pair of the pinned ferromagnetic layers or free ferromagnetic layers. Sputtering may be employed to form the insulating layer of the aforementioned compound. Alternatively, oxygen or nitrogen gas may be introduced to induce the reaction to the surface of the pinned and/or free ferromagnetic layers so as to establish the insulating layer spreading over the surface of the pinned and/or free ferromagnetic layers.
Furthermore, according to a third aspect of the present invention, there is provided a current perpendicular-to-the-plane (CPP) structure spin valve magnetoresistive (MR) transducer comprising: a free ferromagnetic layer; a non-magnetic spacer layer contacting the free ferromagnetic layer over a first interface; a pinned ferromagnetic layer contacting the non-magnetic spacer layer over a second interface; a first insulating layer spaced by the pinned ferromagnetic layer from the non-magnetic spacer layer; and a second insulating layer spaced by the free ferromagnetic layer from the non-magnetic spacer layer.
As mentioned above, the CPP structure spin valve MR transducer of this type allows a sensing current to concentrate at pin-holes formed in the insulating layer. Accordingly, similar to the situation in which the sensing current is allowed to flow through a reduced sectional area, a larger variation can be obtained in response to the inversion of the magnetization in the free ferromagnetic layer in the spin valve MR transducer. Moreover, the spin valve MR transducers of this type is expected to establish a specular reflection or diffusion between the first and second insulating layers. This leads to a still larger variation in the electric resistance in the spin valve MR transducer in response to the rotation of the magnetization in the free ferromagnetic layer.
It should be noted that the CPP structure spin valve MR transducers may be employed in any types of magnetic recording medium drive or storage device such as a hard disk drive.